The conformational and biological activity of chromatin, is dependent on the interactions of the histones, and non-histones with DNA. The condensation of DNA proceeds in at least three levels. Histones condense DNA into globular structures termed nucleosomes; in chromatin nucleosome condense into nucleofilaments, and these condense in a regular array to form the basic chromatin fiber. The factors controlling these levels are not fully understood. The research program to be pursued involves the isolation, biochemical characterization, immunological studies and biophysical analysis of chromatin fragments containing varying number of nucleosomes from chicken erythrocytes. Systematic studies will be made of the conformational features by various biophysical techniques, e.g., circular dichroism, nuclear magnetic resonance, polarization of fluorescence, thermal denaturation, etc. The conformational consequences of the histone:histone interactions in the nucleosome core, the role that Hl/H5 plays in monomer stability and condensation of dinucleosomes and higher oligomers will be explored; as well as naturally modified species. It is anticipated that the existence and structural parameters of the higher levels of DNA organization can be elucidated by employing small oligonucleosomes capable of attaining stable compact structures corresponding to discrete levels of DNA organization. Work will be continued on the role that Hl/H5 plays in condensing the linker DNA to the nucleosome to cause the condensation phenomena. Determination of the structural characteristics required for complete condensation of DNA thus rendering it "inactive," may aid understanding of the process of decondensation and gene activation.